It is well known in the automotive art to provide a variable valve connecting the exhaust manifold with the intake manifold of an internal combustion engine to permit selective and controlled recirculation of a portion of an engine's exhaust gas into the fuel intake stream. Such recirculation is beneficial for reducing the burn temperature of the fuel mix in the engine to reduce formation of nitrogen and sulfur oxides which are significant components of smog. Such a valve is known in the art as an exhaust gas recirculation (EGR) valve. Typically, an EGR valve has a valve body enclosing a chamber disposed between a first port in the exhaust manifold and a second port in the intake manifold; a valve seat dividing the chamber between the two ports; a pintle valve having a valve head fitted to the valve seat and a valve stem or pintle extending from the valve head through a bearing mounted in a third port in a sidewall of the valve body; and an actuator, such as a linear-acting solenoid, mounted on the exterior of the valve body and operationally connected to the outer end of the valve stem. Because exhaust gas may leak along the valve stem, a prior art actuator typically is mounted on standoffs to vent such leaking exhaust gas and thereby prevent it from entering and corroding the solenoid.
The bearing has a circumferential flange for sealing against an outer surface of the valve body and may be urged to seal by a spring which is compressed and captured between the valve body and the actuator, such as a compressed coil spring surrounding the valve stem.
An EGR valve having such a standoff configuration may be exposed to various contaminants, such as mud and salt from roadways, which can corrode the exposed valve stem and spring or accumulate on the bearing, eventually fouling the stem and disabling the valve. Therefore, a cup-shaped bearing splash shield extending axially over the spring and bearing typically is provided to protect the bearing, stem, and spring from external contamination.
During assembly of such a prior art valve, after the valve head is inserted into the chamber via the third port, the bearing is slipped onto the pintle and seated against the valve body, then the spring is installed onto the pintle, then the splash shield is installed over the spring, and then the actuator pole piece is attached to the outer end of the pintle and the actuator is bolted to the valve body through a plurality of hollow standoffs, thus capturing the spring against the underside of the shield and compressing the spring to the proper degree. This procedure requires manual alignment of the various parts, which are loose and which must be mutually aligned for proper assembly; thus, the valve is easily subject to misassembly.
In U.S. Pat. No. 6,634,346, issued Oct. 21, 2003 to Bircann et al., the relevant disclosure of which is herein incorporated by reference, a bearing module is disclosed comprising a pintle bearing, bearing retaining spring, and bearing splash shield for use in an exhaust gas recirculation valve for an internal combustion engine. The bearing is provided with a circumferential flange for sealing with an outer surface of the valve body, and with an annular step for receiving the rolled or crimped skirt of the bearing splash shield. The bearing retaining spring surrounding the valve pintle is compressed and captured within the splash shield as the skirt is formed onto the annular step to form the module. The axial length of the module between the outer end of the shield and the axial face of the bearing flange is slightly greater than the assembled distance between the valve body and the actuator of the EGR valve, such that the spring is further compressed by installation of the actuator onto the valve body to urge the first circumferential bearing face sealingly against the valve body. Advantageously, the prior art bearing module may be pre-assembled offline by known methods to reduce complexity during assembly of the valve.
A portion of the bearing extends into a valve port for the pintle shaft to center the bearing module within the port. In a preferred embodiment of the prior art bearing module, the diameter of the portion of the bearing extending into the valve port is slightly less than the diameter of the port to permit the bearing to shift, or “float”, radially as may be required for the valve head to seat conformably in the seat.
Because the bearing portion extending into the valve port is loose-fitting therein, the seal against leakage between the bearing and the valve body occurs solely at the dynamic interface between the bearing flange and the valve body outer surface. A drawback of the prior art module is that this seal requires a high quality surface on both the valve and the bearing flange, thus adding to the overall manufacturing cost of the valve.
What is needed is a modular assembly of a bearing, spring, and shield which is readily pre-assembled offline, wherein the bearing may be self-aligned by the pintle without resulting in a leak path along the wall of the valve port.